The present invention relates to semiconductor devices and, more particularly, to an insulated-gate bipolar transistor (IGBT) with a current-regenerative diode.
In an inverter circuit, for example, a current-regenerative diode advantageously can be included to form a bypass which permits current flow when an inverse voltage is applied to the switching element in the circuit. As schematically shown in FIG. 4 for an exemplary IGBT switching element 31 with gate electrode G, collector electrode C and emitter electrode E, such a diode 32 is connected in reverse parallel to the switching element.
In the case of a vertical-MOS transistor switching element as shown in FIG. 2, a current-regenerative diode is readily integrated with the switching element. A p.sup.+ -region 23 and a p.sup.+ -channel region 22 are formed at the surface of an n.sup.- -layer 21, with the p.sup.+ -region 23 and the n.sup.- -layer 21 forming a p-n junction in a current-regenerative diode. An electrode 24 making contact with the p.sup.+ -region 23 serves as an anode for the current-regenerative diode, and a transistor drain electrode 26 making contact with an n.sup.+ -drain layer 25 below the n.sup.- -layer 21 serves as a cathode. The electrode 24 and a transistor source electrode 27 are connected by a conductor 28.
In the case of an ordinary bipolar transistor, an integrated current-regenerative diode can be formed by a region of the collector layer and an additional region having the same conductivity type as the base region. On the other hand, in an IGBT with a structure as shown in FIG. 3, an optional buffer n.sup.+ -layer 2 cannot serve in forming a diode because of the p.sup.+ -collector layer 3 below the n.sup.- -layer 1. Further shown in FIG. 3 are a channel p.sup.+ -region 4, an emitter n.sup.+ -region 5 formed at the surface of the channel region, a gate electrode 7 on a gate electrode insulating film 6 laterally extending over a portion of the channel p.sup.+ -region 4 between the emitter n.sup.+ -region 5 and the n.sup.- -layer 1, an emitter electrode 8 contacting both the p.sup.+ -region 4 and the n.sup.+ -region 5, and a collector electrode 9 contacting the collector layer 3.
When, for such an IGBT, a current-regenerative diode is provided on a separate chip, over-all device dimensions are increased, and device manufacture is complicated by the need for additional interconnection and encapsulation.